Detection Of Auditory Steady-state Responses Research Articles

Comparison of sequential test strategies based on Monte Carlo simulations in the detection of auditory steady-state responses

Comparison of sequential test strategies based on Monte Carlo simulations in the detection of auditory steady-state responses

Dealing with correlations in the multichannel EEG using bipolar derivations and Monte Carlo simulations: application to the detection of auditory steady-state responses.

The multichannel objective response detection (MORD) techniques are statistical methods, which use information from more than one electroencephalography (EEG) channel, to infer the presence of evoked potential. However, the correlation level between the channels can lead to a decrease in MORD performance, such as an increase in the false positive (FP) rate and/or a decrease in the detection rate (DR). The present study aims to propose a method to deal with the correlations in the multichannel EEG. The method consists of making an adjustment in the Monte Carlo simulation, considering the information between channels. The MORD techniques with and without the new method were applied to an auditory steady-state response (ASSR) database, composed of the EEG multichannel of eleven volunteers during multifrequency stimulation. The proposed method kept the FP rate at values equal to or less than the significance level of the test and led to an increase of 8.51% in the DR in relation to non-application of the method. Results of this study indicate that the proposed method is an alternative to deal with the effect of the correlation between channels in situations where MORD techniques are applied.

Do cochlear microphonics evoked by narrow-band chirp stimuli affect the objective detection of auditory steady-state responses?

Objective It has recently been discussed whether hearing screening and hearing threshold assessment can accurately be completed using automated ASSR methods for children with auditory neuropathy spectrum disorder (ANSD). Possible causes for the claimed potential failures were investigated here. Design The study is based on the analysis of stored ASSR raw data. Study sample This study reviewed raw ASSR data from 274 patients with a total of 5809 individual recordings. Results Cochlear microphonics (CM) were found in 18 of the 274 patient records. Four of these 18 were obtained from patients with ANSD. One patient with ANSD without click auditory brainstem responses up to 100 dBnHL demonstrated clear ASSR responses from 65 dBnHL upwards. Where click stimulation suggests an auditory nerve defect, narrow-band chirps were shown to evoke ASSR in certain patients. CMs are elicited by narrow-band chirps in the same way as by broadband stimuli. CM residuals as well as a presumed enlarged wave I with absent neural responses, always accompanied by CM, were found as possible causes of misinterpretation at high stimulus levels. A CM detector was created. Conclusions The CM detector, indicating the presence of CM, will prevent misinterpretation of clinical ASSR results.

Towards Real-Time Detection of Auditory Steady-State Responses: A Comparative Study

To objectively evaluate weak neural responses such as auditory steady-state responses (ASSRs) often involves repetitive measurements, after which the accumulated trials are averaged or analyzed by statistical methods to detect a significant response. Such detection methods are often performed off-line on all measured trials. However, the number of required trials, and therefore the measurement time, is often heuristically chosen, and might be suboptimal. In this work, we compared three real-time signal-detection algorithms that could yield improved detection performance, at reduced measurement time. The classical Neyman-Pearson (NP) detector was evaluated by quantifying the signal-to-noise ratio (SNR), and detection probability of ASSRs, as a function of accumulated trial number. We also analyzed the performance of the Bayes factor (BF) to detect ASSRs at different thresholds. Finally, we modified the sequential probability ratio test (SPRT), with a cropped maximum likelihood (ML) estimator, such that it can detect ASSRs (with unknown SNRs) sequentially. We compared the three real-time detectors by using Monte Carlo simulation, and evaluated their performance on detecting ASSRs, generated from the superposition of a pair of amplitude-modulated (AM) tones near 40 Hz in the EEG of nine subjects with normal hearing. The low-order ASSRs (i.e., envelope frequency-following responses) have been sufficiently evaluated in the literature. However, the higher-order ASSRs might reflect further nonlinear mechanisms in the upper ascending auditory pathway. Results show that the real-time detectors can detect not only all low-order ASSRs but also higher-order ASSRs at frequencies with lower SNR. The NP detector yielded the best simulation and actual detection performance. For all subjects, the second-order ASSRs could already be detected with the NP and BF detectors within five trials, but more trials were needed for the modified SPRT detector. In general, higher-order ASSRs require more trials to detect, with the exception of ASSRs near 40 Hz and 80 Hz. In conclusion, compared with traditional off-line detectors, both (real-time) NP and BF detectors showed improved detection performance, and their application in EEG experiments can save valuable measurement time.

An automatic detection method for 40-Hz auditory steady state response and its application in prognosis of comatose patients

ObjectiveWe proposed a 40-Hz auditory steady-state response (ASSR) automatic detection method, and studied the prognosis of comatose patients by combining the 40-Hz ASSR detection results of multiple paradigms of auditory stimulation. MethodsThe 40-Hz ASSR elicitation experiments were carried out on 32 comatose patients, with the detection results used as prognosis predictors. To achieve automatic detection, the detection was modeled as a binary hypothesis test for a sinusoidal waveform with unknown amplitude and phase, based on the generalized likelihood ratio test (GLRT). The patients were followed up for 6 months, and each patient’s outcome was classified as either favorable outcome (severe disability, moderate disability or good recovery) or unfavorable outcome (vegetative state/unresponsive wakefulness syndrome or death) according to the Glasgow outcome scale (GOS). The performance of the prognosis predictors was assessed using the area under the receiver operating characteristic curve (AUC-ROC). ResultsThe largest AUC in univariate analysis involving a single stimulation paradigm was 0.849, while the AUC obtained by combining multiple predictors was increased to 0.966. ConclusionsFor comatose patients, the absence of 40-Hz ASSR in multiple stimulation paradigms may indicate an unfavorable prognosis. Furthermore, the combination of multiple auditory stimulation paradigms may increase the outcome prediction accuracy. SignificanceThe combination of multi-paradigm 40-Hz ASSR automatic detection results may provide a feasible automatic outcome prediction method for comatose patients.

Estimation of auditory steady-state responses based on the averaging of independent EEG epochs

The amplitude of auditory steady-state responses (ASSRs) generated in the brainstem of rats exponentially decreases over the sequential averaging of EEG epochs. This behavior is partially due to the adaptation of the ASSR induced by the continuous and monotonous stimulation. In this study, we analyzed the potential clinical relevance of the ASSR adaptation. ASSR were elicited in eight anesthetized adult rats by 8-kHz tones, modulated in amplitude at 115 Hz. We called independent epochs to those EEG epochs acquired with sufficiently long inter-stimulus interval, so the ASSR contained in any given epoch is not affected by the previous stimulation. We tested whether the detection of ASSRs is improved when the response is computed by averaging independent EEG epochs, containing only unadapted auditory responses. The improvements in the ASSR detection obtained with standard, weighted and sorted averaging were compared. In the absence of artifacts, when the ASSR was elicited by continuous acoustic stimulation, the computation of the ASSR amplitude relied upon the averaging method. While the adaptive behavior of the ASSR was still evident after the weighting of epochs, the sorted averaging resulted in under-estimations of the ASSR amplitude. In the absence of artifacts, the ASSR amplitudes computed by averaging independent epochs did not depend on the averaging procedure. Averaging independent epochs resulted in higher ASSR amplitudes and halved the number of EEG epochs needed to be acquired to achieve the maximum detection rate of the ASSR. Acquisition protocols based on averaging independent EEG epochs, in combination with appropriate averaging methods for artifact reduction might contribute to develop more accurate hearing assessments based on ASSRs.

Improving the detection of auditory steady-state responses near 80 Hz using multiple magnitude-squared coherence and multichannel electroencephalogram

Abstract The detection of auditory steady-state responses (ASSRs) is an important task in hearing sciences. Since the signal-to-noise ratio (SNR) of ASSR is low, only signal processing techniques can reveal the presence of such responses immersed in the background electroencephalogram (EEG). The Objective Response Detection (ORD) techniques are mathematical tools that perform an automatic hypothesis test in frequency domain and the Magnitude-Squared Coherence (MSC) is one of the most efficient univariate ORD technique. For a fixed SNR, the only way of improving the detection power of MSC is by using longer signals. However, recently the Multiple Magnitude-Squared Coherence (MMSC) was developed as a multivariable extension of the MSC technique. This multivariate approach may be used to shorten the data length used for detection by using more EEG channels. Thus, this work aims at investigating the performance of the MMSC in the detection of ASSRs and to compare the results with MSC. The ASSRs were elicited by amplitude modulation pure tones delivered binaurally at 70 dB SPL to 24 volunteers with normal hearing thresholds. The carrier frequencies were 500, 1000, 2000 and 4000 Hz and they were modulated with frequencies near 80 Hz. The maximum detection rate and the minimum average detection time obtained were 95.31% and 146.69 s, respectively, and this result was obtained by MMSC using a set of five electrodes (Fz, Pz, Oz, F4 and T4). This result was significantly better than the best MSC result and represented an overall improvement around 18%. Therefore, it is concluded that the multivariate method MMSC has advantage when applied to the detection of ASSRs evoked near 80 Hz.

Comparison of univariate and multivariate magnitude-squared coherences in the detection of human 40-Hz auditory steady-state evoked responses

Abstract Objective response detection (ORD) techniques for evaluating bioelectrical evoked responses in the electroencephalogram (EEG) are based on statistical criteria rather than on visual inspection. Hence, they do not depend on human evaluation, which is often a subjective approach. Furthermore, since such techniques do not involve heuristic approaches, they may be more easily implemented and used in automatic systems. The Magnitude-Squared Coherence (MSC), together with its recently developed multivariate extension (the multiple magnitude-squared coherence – MMSC), have been pointed out as one of the most efficient ORD techniques for detecting steady-state responses in the EEG. In this work, both MSC and MMSC were applied to EEG signals collected during auditory stimulation in order to allow comparison in the detection of auditory steady-state responses (ASSRs). The stimuli consisted of 40 Hz amplitude-modulated tones delivered binaurally in the intensity of 50 dB SPL (sound pressure level). The best result was obtained by using MMSC in the two-electrode set C4 and Fz. This configuration led to a 0.92-detection ratio, within 111.55 s in average to detect each response and kept the false alarm ratio under 0.05. The average improvement in performance was about 11% when compared to the MSC. These results allow concluding that the detection protocol of 40 Hz ASSRs can be improved by using MMSC in multichannel EEG analysis when compared to the traditional univariate MSC approach.

Kalman Filter Based Estimation of Auditory Steady State Response Parameters.

Auditory steady state responses (ASSRs) are brain responses to modulated or repetitive stimuli that can be captured in the EEG recording. ASSRs can be used as an objective measure to clinically determine frequency specific hearing thresholds, to quantify the sensitivity of the auditory system to modulation, and have been related to speech intelligibility. However, the detection of ASSRs is difficult due to the low signal to noise ratio of the responses. Moreover, minimizing measurement time is important for clinical applications. Traditionally ASSRs are analyzed using discrete Fourier transform (DFT) based methods. We present a Kalman filter based ASSR analysis procedure and illustrate several benefits over traditional DFT based methods. We show on a data set of 320 measurements that the proposed method reaches valid amplitude estimates significantly faster than the state of the art DFT method. Further, we provide two extensions to the proposed method. First, we demonstrate information can be incorporated from multiple recording electrodes by extending the system model. Secondly, we extend the model to incorporate artifacts from cochlear implant (CI) stimulation and demonstrate electrically evoked auditory steady state responses (EASSRs) can be accurately measured.

Towards an optimal paradigm for intraoperative auditory nerve monitoring with auditory steady state responses.

Auditory steady state responses (ASSR) may offer an alternative to brainstem auditory evoked potentials for monitoring of the auditory nerve during surgical procedures. In the current study, we evaluated the influence of noise on ASSR characteristics in total intravenous anesthesia (TIVA). Simulated ASSR in real noise recorded during surgery under TIVA were constructed with known parameters. Influence of amplitude, modulation frequency, averaging sweeps and detection threshold on ASSR were evaluated. High amplitude, more sweeps and a liberal threshold facilitated detection. High amplitude ASSR (80nV) were detected in up to 45% with 16s of data, in 80-90% with 112s. Near-threshold ASSR were detected in 0.8-25%. False positives ranged between 0.3 and 10.3%. Number of sweeps did not influence false positives. Amplitude errors varied between -61 and +39% and improved with more averages but not with different thresholds. Modulation rate demonstrated the strongest influence on all parameters. 110Hz yielded best, 90Hz the worst results. Choice of parameters strongly influences detection and characteristics of ASSR. Optimal parameters enabled detection after 16s in 45%. Due to specific noise characteristics, modulation has a critical impact, which is currently not sufficiently recognized in ASSR studies.

Association of Auditory Steady State Responses with Perception of Temporal Modulations and Speech in Noise

Amplitude modulations in the speech convey important acoustic information for speech perception. Auditory steady state response (ASSR) is thought to be physiological correlate of amplitude modulation perception. Limited research is available exploring association between ASSR and modulation detection ability as well as speech perception. Correlation of modulation detection thresholds (MDT) and speech perception in noise with ASSR was investigated in twofold experiments. 30 normal hearing individuals and 11 normal hearing individuals within age range of 18–24 years participated in experiments 1 and 2, respectively. MDTs were measured using ASSR and behavioral method at 60 Hz, 80 Hz, and 120 Hz modulation frequencies in the first experiment. ASSR threshold was obtained by estimating the minimum modulation depth required to elicit ASSR (ASSR-MDT). There was a positive correlation between behavioral MDT and ASSR-MDT at all modulation frequencies. In the second experiment, ASSR for amplitude modulation (AM) sweeps at four different frequency ranges (30–40 Hz, 40–50 Hz, 50–60 Hz, and 60–70 Hz) was recorded. Speech recognition threshold in noise (SRTn) was estimated using staircase procedure. There was a positive correlation between amplitude of ASSR for AM sweep with frequency range of 30–40 Hz and SRTn. Results of the current study suggest that ASSR provides substantial information about temporal modulation and speech perception.

Phase Stability of Auditory Steady State Responses in Newborn Infants

This study examined the phases of auditory steady state responses (ASSRs) evoked by exponentially amplitude-modulated (AM) tones in 44 newborn infants (within 3 days of birth) and in 15 older infants (within 3 to 15 wks of birth). Our hypothesis was that the phases of the ASSRs would show orderly changes with modulation rate/carrier frequency and that this stability could be used with phase-biasing statistical techniques to augment response detection. Multiple ASSRs were recorded to four modulated tonal carriers with intensities of 50 dB SPL, which were combined and presented simultaneously. The carriers of 0.5, 1, 2, and 4 kHz were modulated at rates between 78 and 95 Hz. Recordings lasted 12.3 mins. Data were analyzed offline with particular attention to phase and its possible exploitation in response detection using a phase-weighted t test (PWT). Population normative phase values were compared with self-normative values. The latter uses phase estimates from ASSRs that are detected at an earlier time to estimate expected phases of ASSRs, which have not yet been detected. This was implemented as an interstimulus phase-weighted t test (iPWT). A secondary analysis compared using fixed test durations where data were evaluated once at the end of the recording with variable test durations where data were evaluated after every sweep. Average phases were not statistically different between the newborn and older infants. The mean ASSR phases across both infant groups were 10°, 36°, 83°, and 110° in the left ear and 78°, 97°, 135°, and 138° in the right ear for the four modulated carriers, respectively. Of a total of 172 detected ASSRs across the four carriers, 63% (109/172), 84% (144/172), and 99% (170/172) of the phase values fell within ±30°, ±45°, and ±90° of the population mean values, respectively. Self-normative phase values were slightly closer to actual measured phases, than population normative values. Compared with the F test, with a fixed duration, the iPWT technique did slightly better (71.7% versus 77.1% detected). Compared with the F test, with variable test duration, test time was reduced using the iPWT technique for normal and weighted averaging by 4 and 2.9 sweeps (66 and 48 secs), respectively, while false-positive rates were maintained. Compared with tests that relied on the F-ratio and a fixed time of 12.3 mins, using variable test times and the iPWT approach resulted in a halving of test time, while slightly improving comparable ASSR detection rates (66.7% versus 72.5%). An inter-ear average phase difference of 52° was found, which was not accounted for by modulation rates used for left/right ears. Converting phase to latency yielded similar results to prior studies. The phase responses of ASSRs evoked by AM tones are stable in newborn and young infants. When using the multiple auditory steady state response (MASTER) technique, it is possible to employ phase-biasing methods to reduce test time and increase detection rates. Using self-normative intrastimulus phase difference values provides better estimated phases than average population phases for purposes of response detection.

Optimal electrode selection for multi-channel electroencephalogram based detection of auditory steady-state responses

Auditory steady-state responses (ASSRs) are used for hearing threshold estimation at audiometric frequencies. Hearing impaired newborns, in particular, benefit from this technique as it allows for a more precise diagnosis than traditional techniques, and a hearing aid can be better fitted at an early age. However, measurement duration of current single-channel techniques is still too long for clinical widespread use. This paper evaluates the practical performance of a multi-channel electroencephalogram (EEG) processing strategy based on a detection theory approach. A minimum electrode set is determined for ASSRs with frequencies between 80 and 110 Hz using eight-channel EEG measurements of ten normal-hearing adults. This set provides a near-optimal hearing threshold estimate for all subjects and improves response detection significantly for EEG data with numerous artifacts. Multi-channel processing does not significantly improve response detection for EEG data with few artifacts. In this case, best response detection is obtained when noise-weighted averaging is applied on single-channel data. The same test setup (eight channels, ten normal-hearing subjects) is also used to determine a minimum electrode setup for 10-Hz ASSRs. This configuration allows to record near-optimal signal-to-noise ratios for 80% of subjects.

A Procedural Framework for Auditory Steady-State Response Detection

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Auditory steady-state responses (ASSRs) in EEG measurements are currently used for reliable hearing threshold estimation at audiometric frequencies. Especially, newborns with hearing problems benefit from this technique, as with this information, diagnosis can be better specified and hearing aids can be better fitted at an early age. Unfortunately, measurement duration is still very long for clinical widespread use due to the lack of efficient signal detection techniques with sufficient robustness against artifacts. In this paper, a simplified procedural framework for ASSR detection is worked out that allows the development of a multichannel processing strategy, starting from a detection theory approach. It is shown that a sufficient statistic can be calculated that best captures the amount of ASSR in the recorded data. The evaluation is conducted using data from ten normal-hearing adults. It is concluded that most single- and multichannel approaches are similar in performance when applied to uncontaminated EEG. When artifact-rich EEG is used, the proposed detection-theory-based approach significantly improves the number of ASSR detections compared with a noise-weighted common EEG channel derivation (vertex–occiput). </para>

Improving Auditory Steady-State Response Detection Using Independent Component Analysis on Multichannel EEG Data

Over the last decade, the detection of auditory steady-state responses (ASSR) has been developed for reliable hearing threshold estimation at audiometric frequencies. Unfortunately, the duration of ASSR measurement can be long, which is unpractical for wide scale clinical application. In this paper, we propose independent component analysis (ICA) as a tool to improve the ASSR detection in recorded single-channel as well as multichannel electroencephalogram (EEG) data. We conclude that ICA is able to reduce measurement duration significantly. For a multichannel implementation, near-optimal performance is obtained with five-channel recordings.

Objective Detection of Auditory Steady-State Responses: Comparison of One-Sample and q-Sample Tests

Auditory steady-state responses (ASSR) are expected to be useful for the objective, frequency-specific assessment of hearing thresholds in small children. To detect ASSR close to the hearing threshold, a powerful statistical test has to be applied. At present, so-called one-sample tests are used. These tests only evaluate the phase, or the phase and amplitude, of the first harmonic, that is, the fundamental frequency. It is shown that higher harmonics with significant amplitudes are also contained in the ASSR spectrum. For this reason, statistical tests that only consider the first harmonic ignore a significant portion of the available information. The use of a q-sample test, which, in addition to the fundamental frequency, also includes higher harmonics in the detection leads to a better detection performance. The evaluation of test performance uses both detection rate and detection time.

Auditory steady-state responses (ASSR): effects of modulation and carrier frequencies

Presented are results relevant to extending the utility of the auditory steady-state response (ASSR) in threshold estimation at high-frequency carriers and to the accuracy of thresholds estimated using modulation frequencies near 40 versus 80 Hz. Initially, efforts were directed at confirming various findings reported in the literature apropos effects of several basic ASSR parameters. Results supplement others’ observations suggesting that ASSR detection limits overestimate behavioral thresholds for conventional audiometric (carrier) frequencies from 500 to 4000 Hz. Further investigation revealed even greater errors of threshold estimates for 8000 and 12 000 Hz, by about 14 and 22 dB on average, respectively. Although suggesting high-frequency ASSR testing to be efficacious, technical advances and additional work is needed to establish clinical utility. Comparison of effects of modulation frequency suggested ASSR thresholds with 40 Hz modulation to fall closer to behavioral threshold than those estimated at 80 Hz. Consequently, when circumstances permit, 40 Hz ASSR testing may be the method of choice (e.g. in the assessment of malingers, who may be tested awake/alert).

The use of phase in the detection of auditory steady-state responses

Objective: To investigate how phase measurements might facilitate the detection of auditory steady-state responses. Methods: Multiple steady-state responses were evoked by auditory stimuli modulated at rates between 78 and 95 Hz and with intensities between 50 and 0 dB SPL. The responses were evaluated in 20 subjects after 1, 2, 4, and 6 min. The responses were analyzed in the frequency domain using 4 different detection protocols: (1) phase-coherence, (2) phase-weighted coherence, (3) F test for hidden periodicity, and (4) phase-weighted t test. The phase-weighted measurements were either based on the mean phase of a group of normal subjects or derived for each subject from the phase of the response at higher intensities. Results: Detection protocols based on both phase and amplitude ( F test and phase-weighted t test) were more effective than those based on phase alone (phase coherence and phase-weighted coherence) although the difference was small. Protocols using phase-weighting were more effective than those without phase-weighting. The lowest thresholds for the steady-state responses were obtained using the phase-weighted t test. Conclusion: Threshold detection can be improved by weighting the detection protocols toward an expected phase, provided that the expected phase can be reliably predicted.